The fabrication of integrated circuit devices generally involves a variety of patterned layers of semiconductor, insulator and conductor materials. This patterning is often carried out by a process of forming one or more thin layers of material followed by removing unwanted portions of the layers. Such removal is generally carried out by exposing portions of the layers to a liquid, gaseous or ionic etching agent to remove the exposed portions of the layers. The nature and composition of the etching agent used to remove the exposed portions of the layers is dependent upon the nature of layer to be removed as well as the nature of the surrounding layers to be retained.
In order to assure that only desired portions are removed, a photolithographic process is often used. In a photolithographic process, a photoresist layer is formed on the surface of the in-process device. The photoresist layer contains a photo-sensitive polymer whose ease of removal is altered upon exposure to light or other electromagnetic radiation. To define the pattern, the photoresist layer is selectively exposed to radiation and then developed to expose portions of the underlying layer to be removed. In practice, a mask is placed between the photoresist layer and a light source or other radiation source. The mask contains a pattern of opaque and transparent sections to selectively block or transmit the radiation. In a positive resist system, the portions of the photoresist layer exposed to the radiation are photosolubilized and the mask is designed to block the radiation from those portions of the photoresist layer that are to remain after developing. In a negative resist systems, the portions of the photoresist layer exposed to the radiation are photopolymerized and the mask is designed to block the radiation from those portions of the photoresist layer that are to be removed by developing.
After developing the photoresist layer, the exposed portions of the underlying layer are removed and then the photoresist layer itself and other post-etch residues are removed. One method for removing or “stripping” such post-etch residues includes contacting the residue with an ozonated aqueous solution. Ozonated aqueous solutions are generally preferred over ashing systems and other solvent-based systems due to ease of use and relatively low environmental concerns. Due to the low solubility of ozone in pure water, however, the water is preferably acidified in order to increase solubility. Such acidification has been accomplished directly, such as adding an inorganic acid to the water, or indirectly, such as formation of nitric acid from nitrogen-containing byproducts in the ozone source gas. While this system is quite acceptable during the patterning of layers such as polysilicon, silicon oxides/nitrides, metal oxides/nitrides and other acid-resistant species, it can become quite problematic where the patterning exposes metal layers. These problems are largely due to the oxidative effect of the ozone and the corrosivity of the acidic solution.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative methods and solutions for removing organic materials in the fabrication of integrated circuit devices.